1. Field of the Invention
The present invention is concerned with processing for reducing random noise in luminance signals and color difference signals originating in an image pickup element system, and further relates to an image pickup system, noise reduction processing device and image pickup processing program which reduce only noise components with high precision, without any influence of the image pickup conditions, by dynamically estimating the amount of noise generated.
2. Description of the Related Art
Noise components contained in digitized image signals obtained from image pickup elements and associated analog circuits (e.g., gain amplifiers) and A/D converters can be divided into the two main categories, fixed-pattern noise and random noise. Fixed-pattern noise is noise that is caused mainly by image pickup elements as represented by defective pixels and the like.
On the other hand, random noise is noise that is generated in image pickup elements and analog circuits, and has characteristics that are close to white noise characteristics. In regard to random noise, as is indicated for example in Japanese Patent Application Laid-Open No. 2001-157057, a method has been disclosed in which the amount of luminance noise is converted into a function with respect to the signal level, the amount of luminance noise for the signal level is estimated from this function, and the filtering frequency characteristics are controlled on the basis of the amount of luminance noise. As a result, appropriate noise reduction processing is performed with respect to the signal level.
Furthermore, in Japanese Patent Application Laid-Open No. 2001-175843, a method is disclosed in which the input signal is separated into luminance and color difference signals, the edge intensity of the image is determined from the luminance signal and color difference signal, and smoothing processing is performed on the color difference signal in regions other than the edge portions. As a result, color noise reduction processing is performed in flat portions.